Anthony, what type and size of rope are you using for the main? Let's make certain you have the correct size and braid of sailing line. Std for an H14 is 3/8" spun braid, 42'. The fuzzy Trophy Braid is pretty popular. Verify that the prior owner didn't substitute a Home Depot rope. If you put the incorrect size or type of braid in those blocks it will not hold.

Next, not sure what you mean about it not clamping the rope as there is no actual clamping movement of the ratchet pulley. I may need you to post a couple of digital pics to see your setup.

Check your ratcheted main block...it should ratchet in one direction only (the direction the line would move when sheeting in) and "not" rotate in the other (the direction the line would move when moving out). I have seen blocks with the cleats installed on the wrong side.

The old style Seaway blocks had a problem with the keeper slipping. Is your main block a Harken or a Seaway?

As far as the Getaway 6:1 main block, any Hobie dealer should stock it. The $70 bucks range was for the main only. You will need a new 2.25" upper in order to go 6:1

Sail fast, Tom G